Bordetella pertussis is the bacterial agent that colonizes the human respiratory epithelium to cause whooping cough. To obtain nutritional iron, B. pertussis produces the siderophore alcaligin and also expresses activities required for utilization of host heme compounds as well as certain non-native siderophores, including the potent siderophore enterobactin. These three iron-retrieval systems have distinct positive transcriptional regulators that respond to the cognate iron source for maximal expression of the genes required for its utilization. The ability of Bordetella cells to selectively express relevant scavenging systems for available iron sources may be important for effective adaptation and multiplication in the host environment. These studies will evaluate the humoral immune response of infected hosts to Bordetella iron system receptors and assess the in vivo importance of each of the three iron uptake systems in animal models of infection. Mechanistic features of siderophore signaling and transcriptional activation will be delineated for the alcaligin siderophore system and the enterobactin siderophore utilization system. The importance of the ability to transcriptionally respond to the appropriate iron source in vivo will be evaluated using Bordetella mutants producing novel hybrid regulators with reversed inducer and target gene specificities. A cell surface signaling phenomenon uniquely involved in regulation of the Bordetella host heme-iron utilization system will be investigated, and interacting signaling and regulatory protein domains will be defined. Spatiotemporal analysis of in vivo expression of the three iron systems will determine which systems are operational in the animal host and assess whether the systems are differentially expressed in certain tissue sites or during distinct stages of infection. Because B. pertussis is an obligate human pathogen with no known environmental or nonhuman animal reservoirs, it represents an ideal model organism for analysis of the host-parasite relationship and the physical, chemical and innate biological conditions that impact on the growth of bacteria in a host environment. This project will provide a better understanding of Bordetella pertussis pathogenic mechanisms and the infection process, as well as host immune responses involved in clearance and protection. [unreadable] [unreadable]